Surface Chemistry of Sputter‐Deposited Al‐Mo and Al‐Cr Alloys Polarized in 0.1N KCl

A study was performed to investigate the changes that take place in the chemistry of the passive film that forms on Al alloys containing either Mo or Cr, as a function of solute concentration and applied potential in . The results show that the mechanisms by which the solute protects the Al alloy differ. Molybdenum forms a film containing that impedes the ingress and movement of the Cl − anion in the film. In contrast, Cr forms a barrier layer that inhibits the oxidation of the Al substrate and restricts the Cl − anions from reaching the metal/film interface. The results show that pitting of Al‐Mo alloys occurs when sufficient is replaced by hydrated Mo +4 compounds, whereas pitting of the Al‐Cr alloys occurs when Cr +3 is oxidized to the more soluble Cr +6 state.